1/11/2016. Types and Characteristics of Microorganisms. Topic VI: Biological Treatment Processes. Learning Objectives:

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1 Topic VI: Biological Treatment Processes Learning Objectives: 1. Discuss microbiology and relate it to wastewater treatment. 2. Describe growth kinetics of pure bacterial culture with Monod expression and MATLAB. 3. Analyze wastewater composition and calculate nutrient requirement for biological treatment. 4. Describe activated sludge processes and their design as well as operation considerations. 5. Discuss kinetic model of activated sludge process and determine parameters using linear regression technique. Reading Assignments: Capter 12 (skip 12.16) and supplement Types and Characteristics of Microorganisms 1

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3 Activated Sludge Process Microbilogy Heterotrophic bacteria Aerobes Autotrophic bacteria Anaerobes Facultative bacteria 3

4 Aerobic: Anaerobic: Metabolism, Energy, and Synthesis Energy Conversions in Anaerobic Metabolism 4

5 Energy Conversions in Aerobic Metabolism Growth Kinetics of Pure Bacterial Cultures 5

6 μ μ m K s S Table 12.1 Approximate Composition Of An Average Domestic Wastewater Before After Biological Sedimentation Sedimentation Treated Total solids Total volatile solids Suspended solids Volatile suspended solids BOD Ammonia nitrogen as N Total nitrogen as N Soluble phosphorus as P Total phosphorus as P Nutrient Requirement for Biological Treatment Mixing Waste Streams 6

7 Example 1: Nutrient Requirements Wastewater 40% coffee wastewater 60% domestic wastewater Coffee Wastewater : 840 mg/l BOD 6 mg/l Total Nitrogen 2 mg/l Total Phosphorus Domestic Wastewater : 200 mg/l BOD 35 mg/l Total Nitrogen 7 mg/l Total Phosphorus If BOD/N/P = 100/6.0/1.5 is required, are the N & P adequate in the combined wastewater? How much pure NH4NO3 and H3PO4 must be added if the nutrient content is insufficient? Wastewater Flow and Strength Variations Example 2: Population Equivalent Domestic wastewater contains 0.24 lb of suspended solids and 0.20 lb of BOD per 120 gal. a. Calculate the suspended-solids and BOD concentrations in mg/l. b. Calculate the BOD equivalent population and the hydraulic equivalent population of an industry that discharges 0.1 mgd of wastewater with an average BOD of 450 mg/l. 7

8 Q, B, S are average annual wastewater flow (mgd), BOD load (lb/day), and SS load (lb/day) respectively. Q m, B m, S m = average flow, BOD, and SS values during the peak month. Q d, B d, S d = average flow, BOD, and SS values for the peak day. Suspended-Growth Treatment Systems 8

9 Waste sludge Return sludge Influent Primary Final Effluent Conventional activated sludge process Fig Conventional Activated Sludge Process (a) Long rectangular aeration tank with submerged coarse-bubble diffusers along one side (Santee, CA) Fig Conventional Activated Sludge Process (b) Cross section of typical aeration tank illustrating the spiral flow pattern created by aeration along one side 9

10 Waste sludge Return sludge Influent Primary Influent Aeration θ=30 ~ 90 min Sed. Effluent Final Effluent Reaeration θ=3 ~ 6 hr Waste sludge Return sludge Step Aeration Activated Sludge process Contact Stabilization without Primary Sedimentation Waste sludge Return sludge Influent Aeration Final Effluent Extended aeration without Primary Sedimentation Table 12.3 General Loading and Operational Parameters for Activated-Sludge Process BOD LOADING AVERAGE PROCESS lb BOD/ lb BOD/ SLUDGE AERATION RETURN 1000 ft 3 / day/lb of AGE PERIOD SLUDGE day a MLSS (days) (hr) RATES (%) Step aeration Conventional (tapered aeration) Contact stabilization Extended aeration High-purity oxygen a 1.0 lb/1000 ft 3 /day = 16 g/m 3.d 10

11 Design and Operation Parameters Example 3: Aeration Tank Design Size a conventional activated sludge process receiving a wastewater flow of 18.2 mgd with 200 mg/l unsettled BOD. Sludge Age (Mean Cell Residence Time) Q Primary Settling Aeration Tank MLSS V Q, SS e Secondary Settling Q R, SS e Q w, SS w 11

12 Example 4: Loading and operational parameters Giving the data below, calculate the loading and operational parameters: settled wastewater flow = 3.67 mgd aeration tank volume = 120,000 ft 3 = mil gal return sludge flow = 1.27 mgd waste sludge flow = 18,900 gpd = mgd MLSS in aeration tank = 2350 mg/l SS in waste sludge = 11,000 mg/l influent wastewater BOD (settled) = 128 mg/l effluent wastewater BOD = 22 mg/l effluent SS = 26 mg/l Kinetic Model of Activated Sludge Process Example 5: Kinetic Constant Determination A municipal wastewater was tested to determine the kinetic constants using a bench-scale unit. Determine the values for Y, k d, k, and K s from the following laboratory data. 12

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14 Loading and Operational Parameters 1. Quantity of air supply to the aeration basin. 2. Rate of activated sludge recirculation. 3. Amount of excess sludge withdrawn to control MLSS in the aeration tank, F/M, and sludge age. 14

15 Rate of metabolism Endogenous phase Good settling characteristics High BOD removal efficiency Declining growth phase Exponential growth phase Poor settling characteristics Poor BOD removal efficiency Range of operation for most activated-sludge-treatment systems Sequencing Batch Reactor (SBR) Food/microorganism Fig Rate of metabolism versus increasing food/microorganism ratio 15

16 Stabilization Ponds, Lagoons, Oxidation Ponds Flat-bottomed pond enclosed by an earth dike. Liquid depth: 2 ~ 5 ft Treat raw or partially treated wastewater. Low BOD loading: 0.1 ~ 0.3 lb/1000 ft 3 /day or 25 ~ 35 lb BOD/acre/day (Northen States), 40 ~ 50 lb BOD/acre/day (Southern States). Long liquid retention times: 50 ~ 150 days Process microbiology: symbiotic relationship between bacteria and algae. O 2 CO 2, NH 3, PO 4 3- Completely Mixed Aerated Lagoons 16

17 Example 6: Aerated Lagoon Size an aerated lagoon to treat a wastewater flow of 0.3 mgd with an average BOD of 600 mg/l. The temperature extremes for the lagoon contents range from 10 C in winter to 35 C in summer. Minimum BOD reduction through the lagoon should be 75%. Fixed Film Biological Process 17

18 Recirculation and sludge return Direct recirculation Influent Primary Filter Final Effluent Influent Primary Filter Filter Final Sludge return Effluent (a) Direct recirculation Recirculation Recirculation Influent Primary Filter Final Effluent Influent Primary Filter Filter Inter Final Sludge return Effluent Sludge return with or without recirculation (b) Fig Typical flow diagrams for two stage trickling filters 18

19 Efficiency Equation for Stone Media Trickling Filters Example 7: Trickling Filter Efficiency Equation For Plastic-Media Tricking Filters Calculate the BOD loading, hydraulic loading, BOD removal efficiency, and effluent BOD concentration of a single-stage trickling filter based on the following data: average raw wastewater flow = 280 gpm recirculation ratio = 0.5 settled wastewater BOD = 130 mg/l diameter of filter = 18.0 m depth of media = 2.1 m wastewater temperature = 18 C 19

20 Design Criteria for RBC Example 8: RBC Area Requirement Calculate the RBC area required for secondary treatment of a raw domestic wastewater having 230 mg/l BOD. The design flow is 2.0 mgd at a temperature of 50 F. 20